Thursday 19 July 2012 12.07 EDT
First published on Thursday 19 July 2012 12.07 EDT

Senior police investigating the death of Ian Tomlinson at the G20 protests failed to inform the police watchdog about three police witnesses who were "adamant" they had seen a colleague attack him before his collapse, an inquiry has concluded.

Detectives at City of London police were told just 48 hours after the newspaper seller's death about witness testimony from three Metropolitan police officers, all of whom were standing beside the 47-year-old when he was struck by PC Simon Harwood.

Upholding a complaint against the force, the Independent Police Complaints Commission said it was not told about the witness evidence until seven days after the death – and only after the Guardian released video footage showing the incident in full.

The watchdog also concluded that the City of London detective superintendent in charge of the investigation, Antony Crampton, made a "poor" decision when he decided not to tell Tomlinson's family about injuries found on his body at a postmortem examination.

In his log book, Crampton justified withholding details about puncture marks found on Tomlinson's leg, and an elongated bruise which a pathologist said may have been caused by a baton strike, because he did not want to cause the grieving relatives "unnecessary alarm or distress". Crampton also noted he could not offer a realistic explanation for the injuries.

The IPCC report said withholding the information was "a poor decision not supported by a specific rationale", adding: "The truth would have inevitably come out." Crampton only reversed his decision two days later, after pictures emerged showing Tomlinson at the feet of riot police and witnesses said they had seen him struck by a baton.

However, the IPCC decided not to uphold the family's complaints against Crampton, saying there was no evidence he intended to mislead them.

Overall, the watchdog said it did not believe City of London police attempted to mislead investigators or the family. The IPCC claimed that any failings on the part of police had no adverse effect on the inquiry, postmortem or inquest.

The IPCC launched its inquiry into the handling of witness information last May, after an investigation by the Guardian revealed that, four days before video footage was released, three police constables – Andrew Moore, Kerry Smith and Nicholas Jackson – told their seniors Tomlinson had been struck with a baton and pushed to the ground.

The breakthrough occurred 24 hours after Tomlinson's death, when Jackson saw newspaper photographs of Tomlinson being treated by medics and recognised him as the same man he had seen pushed to the ground by a police officer. When Jackson was on duty the following day he told his chief inspector, who tracked down Smith and Moore, who confirmed they had seen the same incident.

The crucial information was immediately relayed to City of London police, the small force which has jurisdiction over the Square Mile and was running the investigation.

Detective Chief Inspector Steven Chandler of City of London police, who took the call from the Met police about their three witnesses, initially said he had received the information only after the first postmortem examination had taken place and was therefore unable to relay it to Crampton, who was present during the autopsy, in time.

Mobile phone records proved that Chandler received the call at 4.20pm on 3 April. By the time he tried to relay the information to Crampton, the senior officer's mobile phone was turned off.

The IPCC, which has been criticised for its own role in the Tomlinson inquiry, concluded that the inability to recognise the significance of the three police witnesses, along with two members of the public who came forward at about the same time, was only "a minor failure".

The IPCC rejected almost all of the points raised by Tomlinson's family in a 56-page complaint document listing the apparent investigative failures in the days following his death. None of the officers involved in the investigation was found guilty of any disciplinary offence.

The IPCC report did not substantially address any of the watchdog's own perceived failings, including the fact it declined to begin an independent investigation into Tomlinson's death for more than a week – only taking over the inquiry from City of London police when the Guardian released footage of the attack.

Chris Mahaffey, the IPCC investigator, was aware that at least two witnesses had seen Tomlinson attacked by a police officer. Their accounts corresponded with photographs showing the newspaper seller lying at the feet of riot police in apparent distress. However, the IPCC decided there was insufficient evidence of contact with police.

Its report said: "It was not until 6pm on 7 April when footage of physical contact between a police officer and Mr Tomlinson appeared on the Guardian website that Mr Mahaffey was certain that physical contact between a police officer and Mr Tomlinson had taken place. He considered this a significant development."

Deborah Glass, the IPCC commissioner for London, said: "Had the information about police contact been passed to the IPCC sooner, I have no doubt this would have made a difference to the timing of our decision to carry out an independent investigation – and therefore to the confidence in the IPCC of both the family and those in the public who believe that the IPCC's response to Mr Tomlinson's death was too slow.

"The lack of communication did not affect the integrity of the investigation in the end – but it did damage public confidence in the IPCC, which is at the core of our work."

Glass added that the IPCC no longer deals with cases where there may have been police contact in the same way, adding: "In such circumstances we would now immediately launch an independent investigation into whether there is such a link."

When the IPCC took over the investigation, a meeting was convened with the family and City of London police. When the video was replayed at the meeting, the family were deeply upset when Crampton remarked that the man shown attacking Tomlinson could have been a member of the public dressed in a stolen police uniform.

The family were astonished by the intervention, believing it showed the senior officer who until then had led the inquiry was "either unable to accept the obvious truth or determined to hold on to a falsehood at all costs".

Mahaffey disagreed with the family, saying "the possibility of a police impersonator needed to be explored".